1. Field of the Invention
The present invention relates to a method suitably used for producing reduced metals, such as reduced iron and the like, by heating a metal oxide, such as iron oxide or the like, together with a reducing agent in a combustion furnace, and also to an apparatus for reducing metal oxides.
2. Description of the Related Art
In order to produce reduced iron, i.e., metallic iron, a method is known in which iron oxide is reduced by being heated together with carbonaceous material in a furnace. The furnace known as being used in this case is an electric furnace in which heating is performed by means of electrical energy, and a combustion furnace in which heating is performed by means of combustion heat evolved from fuel.
For example, a method designed to use a combustion furnace is known as disclosed in Japanese Unexamined Patent Application Publication No. 11-061216 and so on. In this method, agglomerates obtained from iron oxide and carbonaceous material, i.e., iron oxide pellets filled with carbonaceous material, are heated by a burner in a rotary hearth furnace, whereby reduced iron is produced. Of the accompanying drawings, FIG. 3 shows, as a schematic view, an apparatus taken up in explaining the production method of reduced iron using the rotary hearth furnace noted above. This apparatus is equipped with a rotary hearth furnace 1 that is constituted of a ring-shaped rotary hearth 2 and a furnace body 3 mounted to cover the rotary hearth 2. By driving means (not shown), the rotary hearth 2 can rotate, i.e., revolve, at appropriate speeds. Carbonaceous material-filled iron oxide pellets 7 are supplied to the rotary hearth furnace 1 through a feed hopper 5 for feedstock charge disposed in the furnace so that they are placed on the rotary hearth 2 and then heated and reduced while the rotary hearth is being traveled in the direction of rotation in the furnace. The pellets 7 thus reduced are taken out of the furnace by discharge means 8 located downstream in the direction of rotation. In the apparatus shown here, such discharge means are structured to be belt conveyor-type discharge means.
In the rotary hearth furnace 1, a plurality of burners 4 are employed as heating means that are positioned on the inner wall surface of the furnace body 3 and along the direction of rotation. Thus, the pellets 7 can be substantially uniformly heated in the furnace. Exhaust gas, i.e., combustion gas, evolved by burner heating is exhausted via an exhaust gas line 6 arranged at a proper portion of the furnace body 3. Subsequently, the exhaust gas is subjected to heat removal by a waste heat-recovery unit (not shown), such as a heat exchanger or the like, followed by temperature control using a temperature control unit and then by dust removal using a bag filter. The exhaust gas after being so treated is released in the air.
However, when iron oxide is reduced by burner heating as mentioned above, general-purpose fuel such as commercially available gas, heavy oil, pulverized coal or the like must be used in large amounts. Namely, mass consumption of combustion heat evolved from the general-purpose fuel is necessary, and as a result, is responsible for poor cost performance.
On the other hand, a method in which organic matter is carbonized by heating is known as disclosed in Japanese Unexamined Patent Application Publication No. 2001-3062. In this method, dry-distilled gas generated while organic matter is being heated is utilized as fuel for a burner used to heat the organic matter. Another method is known as shown in FIG. 4. In the method of FIG. 4, an externally heated kiln 10 is used as a carbonization furnace, and feedstock to be carbonized, i.e., organic matter, is put into the carbonization furnace, i.e., the kiln. After dry-distilled gas generated from the carbonization feedstock is allowed to burn in a combustion furnace, part of the resulting combustion gas is released outside via a temperature control tower and a bag filter, while the remaining gas is supplied to a heat exchanger 11 disposed in the carbonization furnace 10 so that this gas is utilized to heat the carbonization feedstock. However, the amount of heat generated by combustion of the dry-distilled gas is larger than that needed for carbonizing the organic matter. For this reason, the amount of heat having been generated cannot be wholly utilized to advantage and is partly wasted.
Japanese Unexamined Patent Application Publication No. 2000-309780 discloses a method in which large amounts of heat are supplied to a waste material such that the latter is caused to undergo dry distillation and thermal decomposition, and the resulting thermal decomposition solid products and gaseous products are reused, respectively, as fuel. However, the above publication fails to disclose how these solid and gaseous decomposition products are utilized. The publication also discloses using kilns in two stages with a view to avoiding the formation of carbonaceous solid products and gaseous products such as hydrogen, lower hydrocarbons and the like. In such an instance, equipment and facilities are so complicated as to present low cost performance. Moreover, the content of carbonaceous solid products is small so that the resulting thermal decomposition solids are difficult to be used as reducing agents.
The present inventors have conducted extensive research in solving the above-mentioned problems of the conventional art. As a result of this research, it has been found that when a carbonization furnace and a reduction furnace are combined together, reduced metals can be produced with a sharp cut in production cost. More specifically, it has been found that when dry-distilled gas generated during carbonization of organic matter is used as fuel for burner heating in metal reduction, the consumption of general-purpose fuel, such as commercially available gas, heavy oil, pulverized coal or the like, can be greatly saved. This saving in the consumption of general-purpose fuel appears to be attributed to the fact that the metal reduction requires much heat unlike the carbonization of organic matter. Namely, it has been found that when both carbonization equipment and metal reduction equipment are considered as a whole, the overall thermal efficiency can be enhanced with consequential considerable cutting in the production cost of a reduced metal.
With regard to the case where a carbonization furnace and a reduction furnace are used as combined, it has also been found that when a metal oxide is placed in advance in the carbonization furnace, a heat medium such as sand or the like, usually employed in the latter furnace is not required so that no sand separation is needed. Nor are extra process steps necessary for mixing carbonaceous matter and a metal oxide. Hence, feedstock such as a metal oxide, a reducing agent and the like can be prepared with good efficiency, and when both carbonization equipment and metal reduction equipment are considered as a whole, the production cost of a reduced metal can be markedly cut down.
The present invention has been completed based on the foregoing findings.
Accordingly, one object of the present invention is to provide a method of producing reduced metals, which can yield excellent cost performance, and an apparatus for reducing metals oxides.
Another object of the invention is to provide a method of producing reduced metals, such as reduced iron, etc., which can yield excellent thermal efficiency and minimum consumption of combustion heat from general-purpose fuel, and an apparatus for reducing metals oxides.
Yet another object of the invention is to provide a method of producing reduced metals, which can prepare feedstock, such as metal oxides, reducing agents and the like, with good efficiency, and an apparatus for reducing metals oxides.
According to one aspect of the present invention, a method of producing reduced metals from metal oxides is provided which comprises the step of: heating a mixture comprising a metal oxide and a reducing agent by means of a burner, thereby reducing the metal oxide to a reduced metal; wherein dry-distilled gas generated during carbonization of an organic matter-containing component, such as town waste or industrial waste, or solid fuel obtained by treatment thereof, is used as fuel for the burner.
Preferably, in this method, the sensible heat of exhaust gas evolved by the burner is used as heat for carbonizing the organic matter-containing component. Also preferably, carbide derived by carbonizing the organic matter-containing component is used as the reducing agent.
According to another aspect of the present invention, a method of producing reduced metals from metal oxides comprises the steps of: carbonizing an organic matter-containing component to prepare a carbide; and heating a mixture comprising a metal oxide and the carbide, thereby reducing said metal oxide to a reduced metal; wherein said metal oxide is fed together with said organic matter-containing component to carbonization furnace as heat media.
Furthermore, in this method, a metal oxide is caused to coexist as a heat medium when the organic matter-containing component is carbonized in a carbonization furnace, and a mixture of carbide taken out of the carbonization furnace and an organic matter-containing component is reduced in a reduction furnace.
According yet to another aspect of the invention, an apparatus for reducing metal oxides is provided which comprises: a carbonization furnace for carbonizing an organic matter-containing component, thereby generating dry-distilled gas; a reduction furnace, such as a movable hearth furnace, for heating a mixture comprising a metal oxide and a reducing agent by means of a burner, thereby reducing the metal oxide; and a line for supplying the dry-distilled gas to the burner as fuel therefor from the carbonization furnace.
Preferably, in this apparatus, a line for exhausting combustion gas generated by the burner is connected to the carbonization furnace for heat exchange to be performed. Also preferably, a line for supplying carbide taken out of the carbonization furnace is connected to the reduction furnace.